Families ask this constantly, and the honest answer is that the time itself matters much less than what happens inside it.
Deciding on the day is guessing
You have met once, briefly, in a room arranged for the purpose, with both of you performing. Nobody is themselves in that hour. A yes given the same evening is a yes to an impression.
The pressure to decide immediately usually comes from a fear that the other side will lose interest. In practice, no reasonable family withdraws because you took three days.
Three months of meetings is avoiding
At the other end, some families meet repeatedly for months without moving. Each meeting produces less information than the one before, because both sides have run out of new things to show.
If four conversations have not told you, a fifth will not. Something else is going on, usually a doubt nobody has said aloud.
What is actually useful
A few days after the first meeting. Enough to stop performing and notice what you actually think.
Two or three real conversations, without an audience. Phone, video, whatever is acceptable to both families. This is where you learn most, and it is the part most likely to be skipped.
One awkward subject raised deliberately. Money, where you will live, parents, children, work after marriage. Pick the one that matters most to you. How someone handles an uncomfortable question tells you more than everything else combined.
A second meeting, if the first went well. People are noticeably more themselves the second time.
That is typically two to four weeks. Longer if distance makes it slow, which is common and fine.
The signs you are stalling
You keep finding new criteria after each meeting. You are waiting to feel certain. You are comparing against someone hypothetical who has not appeared.
Certainty is not available. What is available is: no serious doubts, a few good conversations, and the sense that this is someone you could build something with. If you have that, waiting longer will not improve it.
The question is not "am I sure". It is "is there anything I am ignoring because I don't want to deal with it".
And when it is a no
Say it quickly. The kindest thing in this entire process is a clear no within a few days, and the cruelest is a maybe that lasts a month.